Enhancing Punching Strength and Deformation Capacity of Flat Slabs

Abstract

A new simplified and yet rational method is proposed to calculate ultimate tendon stress in internally unbonded prestressed concrete (PC) members in this paper. Firstly, a beam-tendon structural deformation model, in which the unbonded tendon is approximated by a number of segments, is proposed to implement global deformation compatibility. Using a geometry analysis, the tendon elongation is expressed as a function of the displacements of the segments. Based on plastic collapse mechanism, a deflected shape is introduced to simplify the deformation curve of unbonded PC members at ultimate limit state. Then, an analytical model is proposed for ultimate stress increase in unbonded tendons. Finally, a straightforward equation is developed to predict the tendon stress increase based on a regression analysis of parametric analysis results. On this basis, a simplified method is proposed to determine the ultimate tendon stress and flexural capacity of simply supported and continuous members. It is found that the proposed method is more accurate than existing methods by comparing their predictions with available experimental results of 218 specimens.